Process And Apparatus For Transferring Heat From A First Medium to a Second Medium

ABSTRACT

A process of transferring heat from a first relatively cold medium to a second relatively hot medium features rotating a contained amount of a compressible fluid about an axis of rotation, thus generating a radial temperature gradient in the fluid, and heating the second medium by means of the fluid in a section of the fluid relatively far from the axis of rotation. An apparatus for carrying out the process includes a gastight drum having a lumen for holding a compressible fluid and rotatably mounted in a frame, and a first heat exchanger mounted inside the drum relatively far from the axis of rotation of the drum.

RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national phase of InternationalApplication No. PCT/EP2008/051752, entitled “PROCESS AND APPARATUS FORTRANSFERRING HEAT FROM A FIRST MEDIUM TO A SECOND MEDIUM” filed on Feb.13, 2008, which claims priority to European Application Serial Number07109194.6, filed on May 30, 2007, and European Application SerialNumber 07102399.8, filed on Feb. 14, 2007.

TECHNICAL BACKGROUND

The invention relates to a process and an apparatus for transferringheat from a first, relatively cold medium to a second, relatively hotmedium.

BACKGROUND

In current power plants, work is typically generated by means of aCarnot cycle or “steam cycle,” employing a high temperature source and alow temperature source (heat sink). In practice, a high temperaturemedium, typically superheated steam, is fed to a turbine, whichgenerates work, and is subsequently condensed, (super)heated and oncemore fed to the turbine. In other words, the difference between theamount of heat contained in the high temperature medium and the amountof heat sunk to the low temperature source is converted into work, inaccordance with the first law of thermodynamics.

At higher temperature differences between the high and low temperaturesources, more heat can be converted into work and the efficiency of theprocess improves. Typically, the environment (earth) serves as the lowtemperature source (heat sink) and the high temperature medium isgenerated by burning fossil fuels or by nuclear fission.

DE 32 38 567 relates to a device for generating temperature differencesfor heating and cooling. Under the influence of an external force, atemperature difference is established in a gas. By using centrifugalforces and with gases of high molecular weight, this effect is increasedto such an extent that it is of interest for technical use.

WO 03/095920 relates to a method for transmitting heat energy, whereinthe heat energy is transmitted into an inner chamber (3) of a rotatingcentrifuge via a first heat exchanger (4, 4a, 4b), in which innerchamber (3) a gaseous energy transfer medium is provided, and whereinthe heat is discharged from the centrifuge (2) via a second heatexchanger (5; 5a, 5b). The amount of energy used can be reducedsubstantially by providing the gaseous energy transmission medium insidethe rotor (12) in a state of equilibrium and by radially orienting theheat flow in an outward direction. It is essential to the inventionunderlying WO 03/095920 that convection be prevented (page 2, lastsentence).

U.S. Pat. No. 3,902,549 relates to a rotor mounted for high-speedrotation. At its center is located a source of thermal energy whereas atits periphery there is located a heat exchanger. Chambers are provided,accommodating a gaseous material which, depending upon its position inthe chambers, can receive heat from the source of thermal energy oryield heat to the heat exchanger.

For the sake of completeness, it is noted that U.S. Pat. No. 4,107,944relates to a method and apparatus for generating heating and cooling bycirculating a working fluid within passageways carried by rotors,compressing said working fluid therewithin and removing heat from saidworking fluid in a heat removal heat exchanger and adding heat into saidworking fluid in a heat addition heat exchanger, all carried by saidrotors. The working fluid is sealed within, and may be a suitable gas,such as nitrogen. A working fluid heat exchanger is also provided toexchange heat within the rotor between two streams of said workingfluid.

U.S. Pat. No. 4,005,587 relates to a method and apparatus for transportof heat from a low temperature heat source into a higher temperatureheated sink, using a compressible working fluid compressed bycentrifugal force within a rotating rotor with an accompanyingtemperature increase. Heat is transferred from the heated working fluidinto the heat sink at higher temperature, and heat is added into theworking fluid after expansion and cooling from a colder heat source.Cooling is provided within the rotor to control the working fluiddensity, to assist working fluid circulation.

Similar methods and apparatuses are known from U.S. Pat. No. 3,828,573,U.S. Pat. No. 3,933,008, U.S. Pat. No. 4,060,989, and U.S. Pat. No.3,931,713.

WO 2006/119946 relates to device (70) and method for transferring heatfrom a first zone (71) to a second zone (72) using mobile (often gaseousor vaporous) atoms or molecules (4) in which in one embodiment, thechaotic motion of the atoms/molecules which usually frustrates thetransfer of heat by simple molecular motion is overcome by usingpreferably elongated nanosized constraints (33) (such as a carbonnanotube) to align the atoms/molecules and then subjecting them to anaccelerating force in the direction in which the heat is to betransferred. The accelerating force is preferably centripetal. In analternative embodiment, molecules (4c) in a nanosized constraint may bearranged to transfer heat by means of an oscillation transverse of theelongation of an elongated constraint (40).

JP 61165590 and JP 58035388 relate to rotary-type heat pipes. U.S. Pat.No. 4,285,202 relates to industrial processes for energy conversioninvolving at least one step which consists in acting on the presence ofa working fluid in such a manner as to produce either compression orexpansion

SUMMARY

It is one object of the present disclosure to provide a process forefficiently generating a high temperature medium.

To this end, one aspect of the process includes rotating a containedamount of a compressible fluid about an axis of rotation, thusgenerating a radial temperature gradient in the fluid, and heating thesecond medium by the fluid in a section of the fluid relatively far fromthe axis of rotation.

Some embodiments further include the step of extracting heat from, i.e.,cooling, the first medium by the fluid in a section at or relativelyclose to the axis of rotation.

The hot and cold media thus obtained in turn can be employed e.g., toheat or cool buildings or to generate electricity by, for example, aCarnot cycle or “steam cycle.”

The efficiency of the process according to the present disclosure can befurther increased if segments, defined in radial direction, of the fluidare thoroughly mixed to obtain an at least substantially constantentropy in these segments and thus improved heat conduction within thefluid.

Also, heat conduction and hence efficiency increases with the pressureand density of the fluid. Thus, pressure is preferably in excess of 2bar (at the axis of rotation), and more preferably in excess of 10 bar(at the axis of rotation). The ratio of pressure at the circumferenceand pressure at the axis of rotation is preferably in excess of 5, andmore preferably in excess of 8.

Instead of transferring heat through conductivity, heat can instead orin addition be transferred through heat capacity and mass flow. To thatend, the first medium and/or the second medium flows along at least oneradius of the contained amount, generating an at least partially radialcirculation in the fluid.

The present disclosure further relates to an apparatus for transferringheat from a first relatively cold medium to a second relatively hotmedium, including a gastight drum rotatably mounted in a frame, and afirst heat exchanger mounted inside the drum relatively far from theaxis of rotation of the drum, for instance in the inner wall of thedrum.

In one aspect of the present disclosure, the apparatus includes a secondheat exchanger positioned at or relatively close to the axis ofrotation.

In another aspect, the apparatus includes one or more at leastsubstantially cylindrical and co-axial walls, separating, in radialdirection, the inside of the drum into a plurality of compartments.

In a further aspect, at least one of the heat exchangers is coupled to acycle for generating work. The further cycle can include an evaporatoror super-heater, which is thermally coupled to the high temperature heatexchanger, a condenser, thermally coupled to the low temperature heatexchanger, and a heat engine. The environment will typically serve as aheat sink, but may also serve a high temperature source, if theoperating temperature of the cycle if sufficiently low.

In yet a further aspect, the compressible fluid is a gas and preferablycontains or consists essentially of a mono-atomic element having anatomic number (Z)≧18, such as Argon, and preferably≧36, such as Kryptonand Xenon.

The invention is based on the insight that, although heat normally flowsfrom a from a higher to a lower entropy and hence from higher to a lowertemperature, in a column of an isentropic, compressible fluid positionedin a field of gravity heat also flows from a lower to a higher entropy.In the atmosphere of the earth, this effect reduces the verticaltemperature gradient from a calculated 10° C./km to an actual 6.5°C./km. Hydropower is based on the same principle.

A reduced heat resistance further enhances heat flow from a lower to ahigher temperature.

In accordance with at least some aspects of the present disclosure,artificial gravity is employed to reduce the length of the column of thecompressible fluid, in comparison with a column subjected merely to thegravity of the earth, and the atmosphere is replaced by a gas allowing amuch higher temperature gradient in the fluid. Mixing is employed toimprove heat conduction within the fluid.

Within the framework of the present invention the term “gradient” isdefined as a continuous or stepwise increase or decrease in themagnitude of a property observed in passing from one point to another,e.g., along a radius of a cylinder.

DESCRIPTION OF DRAWINGS

The invention will now be explained in more detail with reference to thedrawings, which schematically show a presently preferred embodiment.

FIGS. 1 and 2 are a perspective view and a side view of a firstembodiment of the apparatus.

FIG. 3 is a cross-section of a drum used in the embodiment of FIGS. 1and 2.

FIG. 4 is a cross-section of a second embodiment of the apparatus.

FIG. 5 is a schematic layout of a power plant comprising the embodimentof FIG. 4.

FIGS. 6A and 6B are cross-sectional side views of a third embodiment ofthe apparatus.

FIG. 7 is a cross-section of an exchanger unit for use in the embodimentof FIGS. 6A and 6B.

FIG. 8 is a cross-section of an exchanger tube for use in the unit ofFIG. 7.

Identical parts and parts performing the same or substantially the samefunction will be denoted by the same numeral.

DETAILED DESCRIPTION

FIG. 1 shows an experimental setup of an artificial gravity apparatus 1.The apparatus 1 comprises a static base frame 2, firmly positioned on afloor, and a rotary table 3, mounted on the base frame 2. Drivingapparatus, e.g., an electromotor 4, are mounted in the base frame 2 andare coupled to the rotary table 3. To reduce drag, an annular wall 5 isfastened to the rotary table 3, along its circumference. Further, acylinder 6 is fastened to the rotary table 3 and extends along a radiusthereof.

As shown in FIG. 3, the cylinder 6 comprises a center ring 7, two(Perspex™) outer cylinders 8, two (Perspex™) inner cylinders 9 mountedcoaxially inside the outer cylinders 8, two end plates 10, and aplurality of studs 11, with which the end plates 10 are pulled onto thecylinders 8, 9, and the cylinders 8, 9, in turn, onto the center ring 7.The cylinder 6 has a total length of 1.0 meter. FIG. 3 is to scale.

The lumen defined by the center ring 7, the inner cylinders 9, and theend plates 10, is filled with Xenon, at ambient temperature and apressure of 1.5 bar, and further contains a plurality of mixers orventilators 13. Finally, a Peltier element (not shown) is mounted on theinner wall of the ring 7 and temperature sensors and pressure gauges(also not shown) are present in both the ring 7 and the end plates 10.

During operation, the rotary table 3 and hence the cylinder 6 is rotatedat a speed of approximately 1000 RPM. Radial segments of the fluid arethoroughly mixed by means of the ventilators 12, to obtain an at leastsubstantially constant entropy in these segments. In view of the factthat the process is reversible and in view of the thermal isolationprovided by the inner and outer cylinders 8, 9, which isolation enablesconducting substantially adiabatic processes, heat transfer within thecylinder 6, from the axis of rotation to the circumference and viceversa, is substantially isentropic.

Upon rotation, the temperature and the pressure of the Xenon at the endplates 10 increase and the temperature and pressure at the ring 7 drop.When, upon reaching equilibrium, a stepped heat pulse is fed to the gasat the ring 7 by means of the Peltier element, temperature and pressureat the ring 7 increase and, subsequently, temperature and pressure atthe end plates 10 increase, i.e., heat flows from a source having arelatively low temperature (the gas at the ring) to a source having arelatively high temperature (the gas at the end plates).

FIG. 4 is a cross-section of a second artificial gravity apparatus 1.The apparatus 1 comprises a static base frame 2, firmly positioned on afloor, and a rotary drum 6, mounted, rotatable about its longitudinalaxis, in the base frame 2, e.g., by means of suitable bearings, such asball bearings 20. The drum 6 suitably has a diameter in a range from 2to 10 meters, in this example 4 meters. The wall of the drum isthermally isolated in a manner known in itself. The apparatus 1 furthercomprises a driving means (not shown) to spin the drum at rates in arange from 50 to 500 RPM.

The drum 6 contains (at least) two heat exchangers, a first heatexchanger 22 mounted inside the drum relatively far from the axis ofrotation of the drum 7 and a second heat exchanger 23 positioned at orrelatively close to said axis. In this example, both heat exchangers 22,23 comprise a coiled tube coaxial with the axis of rotation andconnected, via a first rotatable fluid coupling 24, to a supply and, viaa second rotatable fluid coupling 25, to an outlet.

The embodiment shown in FIG. 4 further comprises an tube 26, coaxialwith the longitudinal axis of the drum 7 and containing an axialventilator 27 to forcedly circulate the contents of the drum. In thisexample, the drum is filled with Xenon at a pressure of 5 bar (atambient temperature), whereas the heat exchangers 22, 23 are filled withwater.

FIG. 5 is a schematic layout of a power plant comprising the embodimentof FIG. 4, coupled to a cycle for generating work, in this example aso-called “steam cycle.” The cycle comprises an super-heater 30, coupledto the high temperature heat exchanger 22 of the apparatus 1, a heatengine, known in itself and comprising, in this example, a turbine 31, acondenser 32 coupled to the first heat exchanger 23 of the apparatus 1,a pump 33, and an evaporator 34. The steam cycle is also filled withwater. Other suitable media are known in the art.

Rotating the drum will generate a radial temperature gradient in theXenon, with a temperature difference (ΔT) between the heat exchangers ina range from 100° C. to 600° C., depending on the angular velocity ofthe drum. In this example, the drum is rotated at 350 RPM resulting in atemperature difference (ΔT) of approximately 300° C. Water at 20° C. isfed to both heat exchangers 22, 23. Heated steam (320° C.) from the hightemperature heat exchanger 22 is fed to the super-heater 30, whereascooled water (10° C.) from the low temperature heat exchanger 23 is fedto the condenser 32. The steam cycle generates work in a manner known initself

In another embodiment, the apparatus comprises two or more drums coupledin series or in parallel. For instance, in configurations comprising twodrums in series, the heated medium from the first drum is fed to the lowtemperature heat exchanger of the second drum. As a result, heattransfer to the high temperature heat exchanger in the second drum isincreased considerably, when compared to heat transfer in the firstdrum. The cooled medium from the first drum can be used as a coolant,e.g., in a condenser.

In another embodiment, and as an alternative or addition to theaforementioned tube (26), the apparatus comprises a plurality of atleast substantially cylindrical and co-axial walls, separating theinside of the drum into a plurality of compartments. The fluid in eachof the compartments is thoroughly mixed, e.g., by ventilators or staticelements, so as to establish a substantially constant entropy withineach of the compartments and thus enhance mass transport within each ofthe compartments. As a result, an entropy gradient, stepwise andnegative in outward radial direction, is achieved which enables heattransfer from the axis of rotation of the drum to the circumference ofthe drum.

The walls mutually separating the compartments may be solid, thuspreventing mass transfer from one compartment to the next, or may beopen, e.g., gauze- or mesh-like, thus allowing limited mass transfer.The walls may also be provided with protrusions and/or other featuresthat increase surface area and thus heat transfer between compartments.

Instead of transferring heat through conductivity, as in the embodimentsabove, heat can instead or in addition be transferred through heatcapacity and mass flow. An embodiment of an artificial gravity apparatus1 based on heat transfer through heat capacity and mass flow is shown inFIGS. 6A to 8. In this embodiment, the first and second heat exchangerscomprises a plurality of radially extending exchanger units 22A, 23Aevenly distributed, both in axial and in tangential direction, over thesurfaces of the inner walls of the drum 6.

As shown in more detail in FIG. 7, each unit comprises a double-walledexchanger tube 40, shown in cross-section in FIG. 8. Each exchanger tube40 comprises an inlet 41, a central feed tube 42, an outer return tube43 concentric with the feed tube, and an outlet 44. The outer tube 43 inturn is provided on its outer surface with means for enhancing heatexchange, e.g., features, such as fins 45, increasing the outer surfaceof the outer tube 43.

Each unit further comprises a siphon 46 positioned concentrically aboutthe exchanger tube 40 and spanning at least 70%, e.g., about 80% of theradial distance between the walls 6A, 6B of the drum 6. To equalize theentropy inside and outside the siphon 46 at least the inner surface ofthe siphon 46 is provided with features for enhancing heat exchange,e.g., fins 47, increasing the inner surface of the siphon 46.

During operation, a cooling medium, e.g., water, is fed to the exchangertubes 40 that are positioned relatively far from the axis of rotation ofthe drum 6, thus locally cooling the fluid in the drum 6 and locallyincreasing density and decreasing entropy. The dense fluid around theexchangers tubes 22A will be forced outwards by artificial gravity,i.e., co-currently with the water and towards the outer wall 6A of thedrum 6, and caused to spread over its inner surface.

A heating medium, e.g., water, is fed to the exchanger tubes 23A thatare positioned relatively close to the axis of rotation of the drum 6,thus heating the fluid in the drum 6 and locally decreasing density andincreasing entropy. The fluid around the exchangers tubes 40 will bedisplaced inwards (buoyancy) as a result of artificial gravity, i.e.,co-currently with the water and towards the inner wall 6B of the drum 6,and caused to spread over its surface.

These two phenomena together generate a circulation between the heatexchangers, which enhances heat transfer outwards from the heatexchanger 23 relatively close to the axis of rotation of the drum 6 andtowards the heat exchanger 22 relatively far from the axis of rotationof the drum 6.

In this embodiment, the length of the exchanger tubes 22A, 23A, isselected such as to prevent these tubes from reaching the zone of thefluid inside the drum where the temperature is about equal to thetemperature of an associated heat buffer, such as the surroundings ofthe apparatus.

In yet another embodiment, an additional liquid flows, e.g., insideradially extending tubes, from the center towards the circumference ofthe drum, thus gaining potential energy and pressure. The high pressureliquid drives a generator, e.g., a (hydro)turbine, and is subsequentlyevaporated by the relatively hot compressible fluid (e.g., Xenon) at ornear the inner wall of the drum. Vapor thus obtained is transported backto the center of the drum, at least partially by employing its ownexpansion, and condensed by means of the relatively cold compressiblefluid. This embodiment can be used to directly drive a generator.

The invention is not restricted to the above-described embodiments,which can be varied in a number of ways within the scope of the claims.For instance, other media, such as carbon dioxide, hydrogen, and CF₄,can be used in the heat exchangers in the drum. Also, to reducerotational resistance, the drum can be operated in a low pressure orvacuum environment.

1-7. (canceled)
 8. A method of transferring heat from a first relativelycold medium to a second relatively hot medium, the method comprising:rotating a contained amount of a compressible fluid about an axis ofrotation, thus generating a radial temperature gradient in the fluid,and heating the second medium by the fluid in a section of the fluidrelatively far from the axis of rotation.
 9. The method according toclaim 8, further comprising the step of extracting heat from the firstmedium by the fluid in a section at or relatively close to the axis ofrotation.
 10. The method according to claim 8, wherein the first mediumand/or the second medium flows along at least one radius of thecontained amount, generating an at least partially radial circulation inthe fluid.
 11. A heat transfer apparatus for transferring heat from afirst relatively cold medium to a second relatively hot medium, theapparatus comprising: a gastight drum having a lumen for holding acompressible fluid and rotatably mounted in a frame, and a first heatexchanger mounted inside the drum relatively far from the axis ofrotation of the drum.
 12. The apparatus according to claim 11,comprising a second heat exchanger positioned at or relatively close tothe axis of rotation.
 13. The apparatus according to claim 11, whereinthe first and/or the second heat exchanger comprise a plurality of tubesradially extending into the lumen.
 14. The apparatus according to claim13, wherein a siphon is positioned concentrically about at least some ofthe tubes.